Radio resource management in femtocells

ABSTRACT

Certain embodiments provide a Femtocell base station arranged to receive interference notifications from another Femtocell base station and to send an interference remedial command to the other Femtocell base station and/or to one or more further Femtocell base stations.

FIELD

Embodiments described herein relate to the management of radio resourcein a system comprising a plurality of Femtocell base stations.

BACKGROUND

Femtocell base stations, which are also referred to as Home basestations or Home nodeBs or Home eNodeBs when they are implemented in3GPP systems, are base stations with limited range, for example with atransmission radius of only 10 m, for use in indoor environments toimprove coverage and capacity. Femtocell base stations have a limitedrange e.g. limited to a home or office area. As a consequence of thissmall coverage area a network employing Femtocells can reuse frequencies(or more generally resource blocks) more often and thus has increasedcapacity when compared to a network using larger cells.

Besides these benefits to network operators, Femtocells can also be ofbenefit to the end user as they can provide network coverage in areasthat would be devoid of such coverage in the absence of the use of suchFemtocells, for example in buildings through which propagation of anoutside network is impeded. The use of Femtocell base stations isespecially attractive for homes where the signal from the macro-cell maynot be able to penetrate the home, for example due to difficult radiopropagation conditions. In situations where a Femtocell base stationprovides network coverage in an area any user equipment in the coveredarea may establish a connection to the Femtocell base station, ratherthan to an also available macro-cell base station, thereby achievingimproved connection. This not only helps to off-load traffic off themacro-cell but also creates more capacity on top of what the macro-cellhas to offer. Reduced load on the existing macro network by offloadingtraffic to Femtocells helps to improve performance of the macro cellusers. At the same time the capital and operating expenditure of thenetwork operator is reduced.

Capacity improvements in the home can moreover assist network operatorsin rolling out competitive pricing plans e.g. unlimited usage at flatrates to compete with fixed line telephones. The use of Femtocell basestations can be incentivised. Network operators may, for example, beable to reduce call charges, possibly even to such an extent that theyare free of charge to the customer, associated with the use ofFemtocells, as such use will result in better performance/improvement incapacity at a cheaper price/lower usage rates. Thus both the customerand the operator may benefit from the use of Femtocells.

Femtocells are designed to be customer premises equipment. Because ofthe small coverage area of Femtocells a large number of Femtocell basestations may be operated simultaneously, having been deployed in an adhoc fashion. In contrast to the manner in which traditional cellularnetworks are operated it may thus not be possible to carry out elaboratenetwork planning for Femtocells.

As the cost associated with the installation of Femtocell base stationsby a skilled technicians is prohibitive Femtocell base stations aremoreover likely to be installed by end users, most of whom may notappreciate the technical aspects of the installation. Femtocell basesstations are consequently expected to be plug and play type devices thatself configure and self optimize during setup and operation.

Once a Femtocell base station powers on, there are several tasks that itneeds to perform. Firstly a network operator's networks need to bediscovered and the Femtocell base station needs to register itself witha thus discovered network. Registration involves the sending of theFemtocell base stations credentials to an authentication server of adiscovered network. The authentication server then authenticates theFemtocell base station. Subsequent to successful authentication, theoperator's network sends initial configuration parameters. Thetime-tested standard TR-069 titled “CPE WAN Management Protocol” fromthe DSL forum, which is herein incorporated by this reference in itsentirety, may be used for authentication.

The initial configuration of Femtocell base stations does not includeoperational aspects related to Radio Resource Management (RRM), whichcomprises interference management. RRM solutions in which the transmitpower of a Femtocell base station is altered so as to reduceinterference and independently from and without coordination with otherFemtocell base stations are known.

Such standalone solutions, where Femtocell base stations actindependently from each other, may not always be able to provide astable management of radio resources. If two or more Femtocell basestations independently change operating frequency without coordinationto the same new operating frequency, this new frequency is the same fortwo or more Femtocell base stations then the changes made by theFemtocell base stations may not have solved the interference problem.Instead the problem may have been compounded.

Networks employing Femtocell base stations that manage interference inthe above described manner may work well in circumstances exhibitingsparse deployment or low levels of traffic. Such networks may, however,not perform well under dense deployment scenarios or if there issignificant contention for resources. In the latter situations it may bemore desirable to coordinate interference management between Femtocellbase stations.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will in the following be described by way of example onlyand with reference to the accompanying drawings, in which:

FIG. 1 shows an exemplary network comprising a plurality of Femtocellsbase stations;

FIG. 2 illustrates the architecture of an exemplary Femtocell basestation;

FIG. 3 illustrates an algorithm executed in an exemplary Femtocell basestation;

FIG. 4 illustrates an example of a resource block usage table;

FIG. 5A shows an example of a neighbouring list;

FIG. 5B shows another example of a neighbouring list;

FIG. 6 shows an algorithm for creating a neighbouring list;

FIG. 7 shows an example of an interference list; and

FIG. 8 shows an algorithm that may be followed by a Femtocell basestation on receipt of a service request from user equipment.

DETAILED DESCRIPTION

For the purpose of this description, a Femtocell base station (or homeNodeB/home eNodeB in the 3GPP LTE parlance, hereinafter referred to‘HNB’), is considered to be a small-scale user-deployed base stationsupporting a restricted (relative to a full-sized cellular base station)number of connected terminals, offering coverage using licensed spectrumin a small volume approximately the size of a single home. Femtocellbase stations have a limited range, for example with a transmissionradius of as little as 10 m, for use in indoor environments to improvecoverage and capacity. The Femtocell base station may connect via abroadband connection, such as a home broadband connection, to a networkoperator's infrastructure over the Internet. References to Femtocellbase stations are intended to include the above referenced HNBs as wellas limited size cells based on Wireless Metropolitan Area Networktechnologies, such as WiMAX.

According to an embodiment there is provided a system comprising aplurality of Femtocell base stations in communicative contact with eachother via a control channel. The Femtocell base stations are arranged toexchange information suitable for controlling a Femtocell base stationvia said control channel.

The plurality of Femtocell base stations that may be those Femtocellbase stations that are within transmission range of each other. OneFemtocell base station may, for example, assume responsibility for themanagement of resources of the Femtocell base stations it is incommunicative contact. Femtocell base stations may transmit beacons atpredetermined intervals. Other Femtocell base stations withintransmission range from the beaconing Femtocell base station can detectthe transmitted beacons and generate an internal list of all of theFemtocell base station it is in communicative contact with. Duringinitialisation the Network Management System may alternatively oradditionally provide a list of neighbouring Femtocell base stations.Updates of this list may be provided when additional Femtocell basestations become active.

A control channel may be or comprise any means by which Femtocell basestations can exchange information suitable for controlling the operatingparameters of one or more of the Femtocell base stations in the networkthat can communicate with each other through the control channel. Acontrol channel may, for example, be a frequency band or time slotreserved for the exchange of control information, a code associated withthe transmission of control information or any other means by whichinformation for the control of operating conditions in one or more ofthe Femtocell base stations within the system can be exchanged ortransmitted. A control channel may, for example be implemented by usinga particular message format that is recognised by the Femtocell basestations as comprising control information. The control channel may, inone embodiment, moreover make use of a number of resource blocks fromamong the resource blocks available to a Femtocell base station for datatransmission.

Control information may be any information or command that is suitablefor influencing or controlling operating parameters of a Femtocell basestation, in particular such commands and information suitable forinfluencing or controlling the way such a Femtocell base station or aplurality of Femtocell base stations allocate resource blocks for thecommunication with user equipment. Control information may also be of anature that governs the level of transmit power one or more of theFemtocell base stations use when communicating with user equipment. Theadjustment of transmit power can be of particular importance ifinterference is caused by the simultaneous use of one or more resourceblocks by two Femtocell base stations.

The preferred embodiments are not limited to the above mentioned systemcomprising a plurality of Femtocell bases stations but also extends tothe individual Femtocell bases stations that can be used in such asystem. According to a preferred embodiment there is thus provided aFemtocell base station arranged to establish a control channel for theexchange of control information with an equivalent Femtocell basestation or to join an existing such control channel within a network.The Femtocell base station may further be arranged to transmit controlinformation onto and/or to receive control information from the controlchannel.

The Femtocell base station may moreover be arranged to establish thecontrol channel when it powers up and/or when it connects to a networkoperator's network. The control channel may be maintained continuouslyfor a period of time, for example until the Femtocell base stationpowers down.

The Femtocell base station may comprise a receiving means for receivinginformation for establishing the control channel from a networkoperator's Network Management System. The Femtocell base station may bearranged to establish the control channel based on information receivedfrom the network operator's Network Management System. The networkoperator's Network Management System may, for example, provide afrequency, frequency band, time slot information or code, or, put moregenerally, a resource block or resource blocks that is/are to be used toestablish the control channel. The control channel that is establishedmay be a new control channel that does not exist when the Femtocell basestation tries to access it so that the control channel is generated bythe Femtocell base station to allow other Femtocell base stations toexchange control information. It can be envisaged that such a newcontrol channel needs to be established in situations where theFemtocell base station is the first Femtocell base station that contactsa network operator's Network Management System and where other Femtocellbase stations that make this contact later can then join in an exchangeof control information on this control channel. In this case the list ofneighbouring Femtocell base stations received from the networkoperator's network management system may not specify any neighbouringFemtocell base stations. The above discussed establishing of the controlchannel, however, also encompasses the joining of an already existingcontrol channel, for example by a Femtocell base station that contacts anetwork operator's Network Management System after another Femtocellbase station has done so and has established the control channel, asreferred to above.

The control channel may be established via an air interface to allowdirect communication between Femtocell base stations, or via thebackhaul, so that Femtocell base stations can communicate indirectly.The latter way of establishing the control channel enables Femtocellbase stations that may only be able to establish an unreliableconnection via an air interface to communicate with each other in a morereliable fashion. A control channel established via the air interfacemay be operating in the licensed or the unlicensed spectrum.

A Femtocell base station may further be arranged to wirelessly send amessage requesting receipt of reply message that comprises an identifierof Femtocell base stations that have received the message. The Femtocellbase station may determine the signal strength of a received returnmessage and store the identifier of the received return messagealongside the determined signal strength. The message may be sent usinga carrier sense multiple access scheme. Alternatively the message may besent and/or the reply message may be received as a broadcast beaconaccording to the IEEE 802.11 specification of a WLAN system or in abeacon slot according to IEEE 802.15.3a.

The Femtocell base station may further be arranged to transmit anotification of an interference onto the control channel, so that otherFemtocell base stations operating using the control channel may receivethe notification. The Femtocell base station thus does not rely on userequipment for forwarding an interference notification, as is the case insome known systems. The interference notification may, however, be sentfollowing the receipt of a measurement report from user equipment.

The Femtocell base station may further comprise a receiving means or areceiver for receiving control messages from another Femtocell basestation via the control channel and a controller that is arranged toexecute a command received via a said control message.

The preferred embodiments are not limited to hardware arranged toestablish and/or operate a control channel and also extends to methodsof operating such hardware/Femtocell base stations and systemscomprising such Femtocell base stations. According to another preferredembodiment there is thus provided a method of managing a plurality ofFemtocell base stations. The method includes establishing a commoncontrol channel between the plurality of Femtocell base station toenable the exchange of control messages between the plurality ofFemtocell base stations. The control messages may comprise commands thatcan readily be interpreted by a receiving Femtocell base station,wherein the command is of a nature that can control an operatingcondition of the receiving Femtocell base station.

According to another preferred embodiment there is provided a method ofoperating a Femtocell base station. The method comprises establishing acontrol channel enabling communication of the Femtocell base stationwith one or more other Femtocell base stations or joining an existingcontrol channel enabling such communication. The method may furthercomprise transmitting to and/or receiving control information from thecontrol channel.

A local resource manager for co-ordinating a response to a resourceblock management problem and/or an interference problem in a centralisedfashion may further be used. Such a local resource manager may keep arecord of resource blocks allocated by a number of Femtocell basestations to data transmission, for example to and from user equipment,to make it easier for an adequate way of addressing the problem to befound. The local resource manager may, for example store informationthat enables the identification of the source of an interferenceproblem. The simultaneous use of the same resource block by twoFemtocell base stations that have overlapping areas of coverage may, forexample be such a source or cause of an interference and can beidentified by a simple comparison of the resource blocks used for datatransmission by the Femtocell base stations “managed” by the localresource manager. The local resource manager may be a Femtocell basestation itself. The local resource manager may further or instead be ameans that is arranged to determine an action that is likely to cause are-direction of the problem and to send a message including a commandsuitable for putting this action into effect to other Femtocell basestations, for example via the control channel. The action can bedetermined based on information stored by the local resource manager,such as the information referred to above. The information regardingresource blocks that are in use that is stored by the local resourcemanager may relate to those resource blocks allocated by those Femtocellbase stations that are within transmission range of the local resourcemanager. The local resource manager may comprise a list of the Femtocellbase stations that are in communicative contact with it. This list maybe created and updated following and based on the receipt of beaconingsignals transmitted by other Femtocell base stations, if such otherFemtocell base stations transmit frequent beaconing signals. The localresource manager may alternatively base its operation on a list ofFemtocell base stations received from a network operator's NetworkManagement System. The local resource manager may of course also storeinformation relating to the resource blocks the local resource manageritself has allocated for communication. When referring to informationrelating to allocated resource blocks, information relating to atransmit power used by Femtocell base stations in general and/or fortransmissions using a particular resource block, or particular resourceblocks in particular, may also be maintained/stored by the localresource manager.

According to another preferred embodiment there is provided a Femtocellbase station comprising a controller arranged to query the presence of aFemtocell base station acting as a local resource manager. Thecontroller may, for example, be arranged to send a query requestinginformation on whether or not another Femtocell base station acts aslocal resource manager to a network operator's network resource manager.The network operator's network resource manager may, in return providean indication of other Femtocell base stations operating in the vicinityof the querying Femtocell base station and whether any one of any suchother Femtocell base stations already fulfils the function of the localresource manager. The Network Resource Manager may, for exampleestablish if one of the Femtocell base stations in the list ofneighbouring Femtocell base stations acts as a local resource manager.

A local resource manager may be a Femtocell base station that may bearranged to monitor the use of communication and/or transmissionresource blocks that are available to Femtocell base stations forcommunication. The local resource manager may additionally or instead bea Femtocell base station that is arranged to send control information,control messages or control commands to other Femtocell base stations,for example via a control channel provided for this purpose. The controlinformation/messages/commands may be designed to be interpreted by otherFemtocell base stations (which may be of the same or similar type as theFemtocell base station that acts as the local resource manager) ascommands or instructions to allocate particular resource blocks orchange an already existing allocation of resource block to a particularcommunicative connection, for example so that other resource blocks areused for operating the communicative connection.

The use of a local resource manager avoids the scalability problemsassociated with a purely centralised solution operating at the networkoperator's Network Management System as the number of Femtocells thatcould potentially belong to an overlapping interference region would bemuch smaller due to the localised effect of interference.

The use of a local resource manager may further allow a networkoperator's management system to influence the Femtocell base stationsmanaged by the local resource manager through the local resourcemanager. Such influencing may be less computationally expensive for theNetwork Management System than having to influence each Femtocell basestation separately, as would have to be the case in a completelydistributed system that does not have a local resource manager that actsin the above described Master-Slave configuration.

The network operator's Network Management System is aware of theFemtocell base stations that operate in a particular area. The NetworkManagement System can accordingly provide a reliable indication of theFemtocell base stations operating in the vicinity of a newly connectingFemtocell base station and of the functions such previously connectedFemtocell base stations fulfil. The Network Management System maytransmit a list of Femtocell base stations that operate in the vicinityof the newly registering Femtocell base station to the newly registeringFemtocell base station upon connection. Updates indicating Femtocellbase stations that have started operation later may be provided as therelevant information becomes available.

The Femtocell base station may further be arranged to establish or jointhe control channel for communication with other Femtocell basestations, as described above. This control channel may be establishedbased on information received from a Network Management System of anetwork operator following the Femtocell's connection to the network.The presence or absence of a Femtocell base station acting as a localresource manager may be queried via said control channel.

The Femtocell base station may further be arranged to operate in a localresource managing mode in which a function for sending commands to otherFemtocell base stations for resource management is enabled. This modemay be entered if the query provides no indication of the presence of alocal resource manager. There may, for example, be no response to thequery or a response to the query may indicate that there is no Femtocellbase station that acts as a local resource manager known to the NetworkManagement System. In this case the Femtocell base station takes overresponsibility for managing the resources of itself and of any Femtocellbase stations that may later start operating in the vicinity, forexample as defined by the list of neighbouring Femtocell base stationsreceived from the network operator's Network management System and byupdates to this list.

The Femtocell base station may further or alternatively be arranged tooperate in a command acceptance mode in which a function in which theFemtocell base station accepts and executes commands received fromanother Femtocell base station is enabled, should the query provide anindication of the presence of a local resource manager. In this case theFemtocell base station is in a mode in which it allows the localresource manager to direct the use of resource blocks via commandsreceived from the local resource manager.

According to another embodiment there is provided a method of joining anetwork. The method is performed in a Femtocell base station andcomprises connecting the Femtocell base station to a core network of anetwork operator and causing the Femtocell base station to send a queryregarding the presence of a local resource manager via a controlchannel. The local resource manager may, for example, be anotherFemtocell base station.

The Femtocell base station may further be switched to a local resourcemanaging mode in which a function for sending commands to otherFemtocell base stations for resource management is enabled if a responseto the query indicates that no Femtocell base station acts as a localresource manager or if no query response is received after apredetermined time. The method may alternatively comprise switching theFemtocell base station to a command acceptance mode in which a functionin which it accepts and executes commands received from anotherFemtocell base station is enabled.

Femtocell base stations managed by a local resource manager so that thelocal resource manager may keep an up-to-date list of allocated resourceblocks.

According to an embodiment there is provided a Femtocell base stationarranged to receive messages from other Femtocell base stationsindicating the allocation or de-allocation of a resource block by theother Femtocell base station and to maintain a record of resource blocksindicated as having been allocated by received messages. A record ofallocated resource blocks relating to a resource block indicated ashaving been de-allocated by a received message may be removed from arecord of allocated resource blocks following receipt of the message.This Femtocell base station consequently fulfils the above describedmonitoring function of the local resource manager. Keeping an-up-to daterecord of allocated resource blocks in a Femtocell base station enablesproviding a response to any interference problems that may arise. Such aresponse can be based on information relating to all Femtocell basestations that may be affected by the interference problem and/or allFemtocell base stations that may be contributing to the problem. Theabove described problems can thus be addressed in a centralised mannerbased on the up-to-date records.

It will be appreciated that the local resource manager needs otherFemtocell base stations to notify the local resource manager of theallocation or de-allocation of resource blocks as they occur. Accordingto another embodiment there is provided a Femtocell base stationarranged to send, via a control channel, a control message for notifyinganother Femtocell base of an allocation or de-allocation of a resourceblock after said resource block has been allocated or de-allocated.

The local resource manager may also send commands controlling theallocation of resource blocks to other Femtocell base stations withwhich it is in communicative contact. According to another embodimentthere is provided a system comprising a plurality of Femtocell basestations in communicative contact with each other, wherein one of theFemtocell base stations is arranged to manage or partially manage, inuse, the allocation of resource blocks of two or more of the pluralityof Femtocell base stations. Partial management may be management that isperformed to overcome a problem, such as, for example an interferenceproblem.

The Femtocell base station managing the resource block may be any of theabove discussed Femtocell base stations. The resource block managing

Femtocell base station and one or more further ones of the plurality ofFemtocell base stations may be in communicative contact with each othervia a dedicated common control channel.

According to another embodiment there is provided a method of operatinga communication system comprising a plurality of Femtocell basestations. The method comprises allocating, in a first Femtocell basestation, a resource block for signal exchange between the firstFemtocell base station and equipment communicatively coupled to theFemtocell base station or de-allocating a previously allocated suchresource block. The method further comprises sending a message from thefirst Femtocell base station to a second Femtocell base station. Themessage comprises information notifying the second Femtocell basestation of the allocation or de-allocation of the resource block. Arecord of notified allocations is maintained in the second Femtocellbase station. Such maintaining may comprise removing allocationinformation following the receipt of a message indicating thede-allocation of a resource block.

According to another embodiment there is provided a system comprising aplurality of Femtocell base stations, wherein one of the plurality ofFemtocell base stations is arranged to, upon allocation or de-allocationof a resource block, transmit a message via a communication channelnotifying another Femtocell base station from among the plurality ofFemtocell base stations of the allocation or de-allocation of theresource block. The other of the Femtocell base station is arranged tomaintain a record of allocated resource blocks.

The other Femtocell base station may further be arranged to, if amessage received from the one Femtocell base station notifies the otherFemtocell base station of the allocation of a resource block, include arecord of the notified allocation of the resource block in the record ofallocated resource blocks. The other Femtocell base station may moreoverbe arranged to, if a message received from the one Femtocell basestation notifies the other Femtocell base station of the de-allocationof a resource block, remove an indication that the resource block hasbeen allocated by the one Femtocell base station from the record ofallocated resource blocks.

According to another embodiment there is provided a system comprising aplurality of Femtocell base stations, wherein at least one of theFemtocell base stations is arranged to maintain a record of resourceblocks allocated by the Femtocell base stations of the plurality ofFemtocell base stations.

According to another embodiment there is provided a method of managingthe allocation of resource block in a system comprising a plurality ofFemtocell base stations. The method comprises the allocation orde-allocation of a resource block by a Femtocell base station and thetransmission of a message onto a communication channel to notify anotherFemtocell base station that maintains a record of allocated resourceblocks of the allocation or de-allocation of the resource block by theFemtocell base station. The other Femtocell base station may be amanaging Femtocell base station.

In case the notification indicates that a resource block has beenallocated, the method may comprise including a record of the notifiedallocation of the resource block in the record maintained by themanaging Femtocell base station. If the notification indicates thede-allocation of a resource block the method may comprise removing arecord of a previous allocation of the resource block from the recordmaintained by the managing Femtocell base.

According to another embodiment there is provided a method of managingresource blocks comprising receiving at a Femtocell base stationinformation of the allocation or de-allocation of a resource block andentering or removing a record of the allocation in or from a record ofall notified resource block allocations.

It will be appreciated that, for example based on the records kept inthe above described manner, it is possible to determine a remedialaction for an interference problem that may be experienced by userequipment or by a Femtocell base station. According to anotherembodiment there is provided a Femtocell base station arranged toreceive interference notifications from another Femtocell base stationand to send an interference remedial command to the other Femtocell basestation, to other Femtocell base stations or to one or more furtherFemtocell base stations. The interference remedial command thus does nothave to be directed towards the Femtocell base station that has providedthe original interference notification.

The Femtocell base station may be arranged to receive the interferencenotification via a dedicated signalling control channel, such as theabove discussed signalling control channel, and/or be arranged to sendthe interference remedial command via a dedicated signalling controlchannel.

The Femtocell base station may further be arranged to determine, using arecord of resource block that have been allocated by other Femtocellbase stations, an action for reducing or eliminating an interferencenotified in said interference notification and to send a message forputting the determined action into effect in another Femtocell basestation as part of the interference remedial command.

According to another embodiment there is provided a Femtocell basestation arranged to receive interference notifications from anotherFemtocell base station and to determine, using a record of resourceblock that have been allocated by other Femtocell base stations, anaction for reducing or eliminating an interference notified in saidinterference notification.

According to another embodiment there is thus provided a Femtocell basestation arranged to receive an interference remedial message comprisingor consisting of a command, the base station comprising a processorarranged to execute the command. The command may be a command toallocate, de-allocate or re-allocate a resource block used by theFemtocell base station. The command may thus, for example, be a commandcausing the Femtocell base station to change a resource block orresource blocks used in a communication link with user equipment toanother resource block or to other resource blocks, thereby potentiallyavoiding an interference problem that the reallocation of the resourceblock is intended to alleviate. The command may alternatively oradditionally be a command for the amount of power used by the Femtocellbase station for one or more particular communicative connections to bealtered. The command may, for example be a command for the transmitpower used in communicating with one or more particular pieces of userequipment to be lowered, thereby again potentially reducing aninterference problem.

Embodiments also extend to the Femtocell base stations from which aninterference remedial command originates. According to anotherembodiment there is thus provided a Femtocell base station arranged tosend, to another Femtocell base station, a command for the otherFemtocell base station to allocate or reallocate a resource block or forthe other Femtocell base station to alter a transmit power.

According to another embodiment there is provided a method of managinginterference in a system comprising a plurality of Femtocell basestations. The method comprises directly sending a message from oneFemtocell base station to another Femtocell base station via a dedicatedcontrol channel. The message provides details of an interference or anundesirable or insufficient service level experienced by or notified tothe one Femtocell base station. A known interference can thus benotified to other Femtocell base stations, such as for example to aFemtocell base stations acting as a local resource manager, as discussedabove, so that remedial action can be fashioned so that it coordinatesresponses to the interference problem between a number of the pluralityof Femtocell base stations.

The method may further comprise determining an action for alleviatingthe interference or for improving the service level in the otherFemtocell base station. This action may be determined in one of theFemtocell base stations receiving the interference notification via thededicated control channel. The Femtocell base station determining theaction may, for example, be a Femtocell base station acting as a localresource manager, as described above.

The method may further comprise sending a further message from theFemtocell base station that has received the interference notificationvia the control channel to the Femtocell base station that hadoriginally sent the interference notification or to a further Femtocellbase station. The further message may comprise a command for putting theaction into effect in the receiving Femtocell base station or Femtocellbase stations. The action may then be performed in the Femtocell basestation that has received the message based on the contents of themessage.

According to another embodiment there is provided a system comprising afirst Femtocell base station and a second Femtocell base station. Thefirst Femtocell base station is arranged to send a message to the secondFemtocell base station. The message comprises a command for changing theallocation of a resource block used by the second Femtocell base stationor for altering a transmit power used by the second Femtocell basestation. The message may, for example, comprise a command for the secondFemtocell base station to alter a transmit power used in one or moreparticular connections to user equipment or used in a particular datatransmission. The first Femtocell base station may further be arrangedto receive messages identifying an interference in data transmission,such as interference experienced by user equipment or by anotherFemtocell base station.

The first Femtocell base station may further be arranged to determine,based on a record of resource blocks allocated by Femtocell basestations with which the first Femtocell base station is in communicativecontact, an action for reducing an identified interference. It will beappreciated that any such action may not guarantee that the interferenceis reduced or even eliminated. The action will however, be an actionthat is likely to lead to a reduction in or an elimination of theinterference. The action may again be notified to the Femtocell basestation that is to implement it in the form of a message transmittedfrom the first Femtocell to another Femtocell base station that isintended to put the action into effect.

According to another embodiment there is provided a system comprising afirst Femtocell base station and a second Femtocell base station, thefirst Femtocell base station arranged to, in response to obtaininginformation of an interference, send a message identifying theinterference to the second Femtocell base station. The second Femtocellbase station is arranged to determine an action for reducing theidentified interference. The action is determined based on a record ofresource blocks allocated by Femtocell base stations with which thesecond Femtocell base station is in communicative contact.

According to another embodiment there is provided a method of managinginterference in a system comprising a plurality of Femtocell basestations. The method comprises sending a message from one Femtocell basestation to another Femtocell base station. The message comprises acommand for execution by the other Femtocell base station, wherein thecommand is intended to alleviate a known interference or to improve aservice level when executed by the other Femtocell base station. Acommand intended to alleviate an interference is one that, based onavailable information, is more likely to reduce a level of interferencethan it is to increase the level of interference or to keep it constant.

The method may further comprise determining a source of interferenceusing a record of resource blocks that have been allocated by theplurality of Femtocell base stations. An action for alleviating theinterference may be determined based on the record. A command forcausing execution of the action in the other Femtocell base station maybe included in the message. Execution of the command in the otherFemtocell base station may alter the allocation of resource blockswithin the other Femtocell base station and/or alter the transmit powerof the other Femtocell base station.

The method may further comprise sending a message from the otherFemtocell base station to the one Femtocell base station confirmingexecution of the command. A record may then be updated to reflectchanges caused by the execution of the command. The record that is beingupdated may, for example, be a record of the resource blocks used by aplurality of Femtocell base station, including the other Femtocell basestation, as discussed above. The record may additionally oralternatively be a record of a power level used in a particular datatransmission.

According to another embodiment there is thus provided a Femtocell basestation arranged to note an interference and to send informationrelating to the interference from the Femtocell base station onto acontrol channel established for exchanging control information.

Embodiments also extend to a method practiced in a system comprising aplurality of communicatively linked Femtocell base stations. Accordingto another embodiment there is provided a method of interferencemanagement comprising receiving at a Femtocell base station informationrelating to an interference, determining a source of the interferencefrom a record of resource blocks allocations, determining, based on therecord, an action for alleviating the interference and generating amessage for sending to another Femtocell base station. The messagecomprises a command suitable for causing execution of the action in theother Femtocell base station.

Embodiments also extend to a method of operating a Femtocell basestation that receives a command intended to put into effect an actionintended to alleviate or eliminate an interference situation. Accordingto another embodiment there is thus provided a method of interferencemanagement. The method comprises receiving at a Femtocell base station amessage comprising a command that, when executed in the Femtocell basestation, causes a change in the allocation of resource blocks within theFemtocell base stations and/or a change in a transmit power level usedfor communicating with user equipment. The method further comprisesexecuting the command in the Femtocell base station.

The change in allocation may comprise one or more of: changing one ormore resource blocks allocated to user equipment and allocating a newresource block to user equipment. A message relating to the interferencemay be sent prior to receipt of the message comprising the command.

According to another embodiment there is provided a Femtocell basestation comprising a memory and arranged to dynamically create and storea list of a plurality of neighbouring Femtocell base stations and, fortwo or more of the neighbouring Femtocell base stations, an indicationof a likelihood that said neighbouring Femtocell base station causesinterference, wherein Femtocell base station is arranged to, in use,create the list through direct wireless communication with anotherFemtocell base station of the same type. The likelihood that theneighbouring base station causes an interference may be expressed interms of the signal strength the Femtocell base station storing the listreceives from the listed Femtocell base station. The likelihood that theneighbouring Femtocell base station causes an interference may bedifferent for different resource blocks and an individual indication ofthis likelihood may be stored for each resource block, so that theneighbouring Femtocell base station that is least likely to causeinterference can be determined individually for each resource block.

The Femtocell base station may further be arranged to maintain a list ofcommunication resources available for use by the Femtocell base stationand to maintain a record of those said communication resources that havebeen allocated for communication by the said Femtocell base station orby one or more of the plurality of neighbouring Femtocell base stations.The Femtocell base station is in this case arranged to determine, basedon the record, whether a the communications resource is unallocated uponreceipt of a request for allocation of a communications resource or uponnotification of an interference in an ongoing communications process. Ifan unallocated communications resource is determined to be available theFemtocell base station may be arranged to allocate the unallocatedcommunications resource.

The Femtocell base station may further be arranged to allocate analready allocated communications resource to the ongoing communicationprocess or to the request, wherein the Femtocell base station isarranged to select as the already allocated communications resource acommunications resource indicated by the record as having been allocatedby the said neighbouring Femtocell base that is least likely to causeinterference.

The Femtocell base station may further be arranged to negotiate, theneighbouring Femtocell base station that is least likely to causeinterference, a level of transmit power that is to be used fortransmission on the already allocated communications resource.

According to another embodiment there is provided a Femtocell basestation arranged to maintain a list of communication resources that are,in use, available to the Femtocell base station and a record of those ofthe communication resources that, in use, have been allocated forcommunication by the Femtocell base station or that have been reportedas having been allocated for communication by another Femtocell basestation. The Femtocell base station is arranged to determine, based onsaid record, whether a said communications resource is unallocated uponreceipt of a request for the establishing of a communication link orupon determination of the presence of an interference in an ongoingcommunications process and, if an unallocated communications resource isdetermined to be available, to allocate said unallocated communicationsresource.

According to another embodiment there is provided a system comprising aplurality of Femtocell base stations, wherein one or more of theplurality of Femtocell base stations is as described above.

According to another embodiment there is provided a method of operatinga system comprising a plurality of Femtocell base stations. The methodcomprises, in more than one of the Femtocell base stations, dynamicallymaintaining a list of communication resources allocated by the Femtocellbase station maintaining the list and by one or more other Femtocellbase stations from among the plurality of Femtocell base stations andchecking based on the list and in response to the receipt of a requestfor the establishing of a communication link or upon determining thepresence of an interference, whether or not an unallocated communicationresource is available.

The method may further comprise maintaining an indication of thelikelihood of interference of the neighbouring Femtocell base stationsand allocating a communication resource that is indicated by the list asalready being allocated in response to the receipt of the request orindication, wherein the communication resource allocated is acommunication resource indicated by the list as having been allocated bythe neighbouring Femtocell base station that is least likely to causeinterference.

Any of the above described Femtocell base stations may be LTE Femtocellbase stations.

The embodiments described in the following are based on the followingassumptions:

-   -   In some embodiments a list of neighbouring Femtocells base        stations is passed as a configuration parameter during the        configuration process initiated on power ON of a Femtocell.        Femtocell base stations of some other embodiments, however, are        arranged to generate the neighbouring list autonomously without        support from the network operator.    -   A control channel for the exchange of signalling/control        information between Femtocell base stations in the list of        neighbouring Femtocell base stations can be established or        exists. This control channel may be created in any known way of        creating a communications channel, for example directly between        Femtocell base stations or via the backhaul IP network. The term        control channel encompasses any such connection, as long as it        is suitable for conveying control information between Femtocell        base stations.    -   For simplicity and without loss of generality it is assumed in        some embodiments that the first Femtocell base station (from the        list of neighbouring Femtocell base stations) to power ON will        assume the responsibility of the local resource manager (LRM).        There may be other ways of selecting/electing an LRM and these        fall within the scope of the embodiments. Other criteria for the        selection of a Femtocell base station as local resource manager        may be hardware/processing capability of the Femtocell base        station knowledge of the fact that a particular Femtocell base        station remains switched ON for long periods (based, for        example, on historical information) etc. Other embodiments        described in the following do not comprise a local resource        manager and instead manage resources in a distributed fashion,        which several or all Femtocell base stations being arranged to        make resource allocation decisions.    -   Femtocell base station communicating in the arrangement        described in the following belong to the same operator. The        issue of non-compliance do therefore not arise and the described        Femtocell base stations obey orders from the local resource        managing Femtocell base station.

FIG. 1 illustrates a distributed system in which four Femtocells 10, 15,and 25 are located in a macrocell 30. Each Femtocell 10, 15, 20 and 25is generated by a corresponding Femtocell base station 35, 40, 45 and 50respectively. Also shown is user equipment 55 located in Femtocells 20and 25. User equipment 60, located in Femtocell 25 is also shown. Theuser equipment 55 and 60 may be cellphones, PDAs, laptops etc. It willbe appreciated that, if user equipment 55 is in communicative contactwith Femtocell base station 45 using a particular communicationsresource, and if the Femtocell base station 50 uses the samecommunications resource to communicate with user equipment 60, then userequipment 55 will experience interference from Femtocell base station50.

In the following two principal embodiments are described for alleviatinginterference. In the first principal embodiment a Femtocell base stationcan receive a list of neighbouring Femtocell base stations from thenetwork operator, for example upon activation of the Femtocell basestation. In another principal embodiment the Femtocell base stations canacquire the list of neighbouring Femtocell base stations in anautonomous fashion without the help of the network operator. TheFemtocell base stations may be in communicative contact with each othervia a control channel. Such a control channel may be associated with aparticular frequency selected from an available frequency spectrum, aparticular transmission timing, code or space.

One of the Femtocell base stations may act as a local resource manager,directing the resource allocation decisions made by other Femtocell basestations communicating with the local resource manager via the controlchannel, either for each allocation of a resource or in case ofinterference, when a coordinated allocation approach is desirable. Sucha local resource manager exclusively operates as master in a masterslave mode together with other Femtocell base station. Alternativelyseveral or each of the Femtocell base stations may be arranged toallocate resources locally but taking into account the resourcerequirements of other Femtocell base stations.

The preferred embodiment reduces the risk of such interference byallocating communications resources based on knowledge of interferencestrength from neighbouring Femtocell base stations and/or knowledge ofthose communication resources that have already been allocated by aFemtocell base station.

Each Femtocell base station 20 may be implemented in hardware as shownin FIG. 2. FIG. 2 illustrates the Femtocell as a wireless access point100 comprising a medium access controller 110 for establishing awireless connection to user equipment or to other Femtocell basestations using an antenna 120 and means 130 for connection to thebackhaul, a WAN and/or a public land mobile network (PLMN). Mediumaccess controller 110 and the means for connecting to the backhaul 130are shown to be communicatively coupled to a communications bus 140. TheFemtocell base station further comprises a processor 150 and a workingmemory, such as RAM and ROM, 160. Optionally additional input/outputdevices 170, such as for example for indicating an operating status orcondition of the Femtocell base station to a user and/or to enable auser to input commands into the Femtocell base station are alsoprovided. Resource allocation lists, neighbouring lists and interferencelists, all discussed in more detail below, may be stored in the workingmemory 160.

Turning now to an embodiment in which one Femtocell base station, out ofa plurality of Femtocell base stations, acts as a local resource managerthat directs the allocation of resources by other Femtocell basestations out of the plurality of Femtocell base stations, FIG. 3outlines the steps a Femtocell base station that is capable of acting asa local resource manager takes upon power up. At step 200 the Femtocellbase station powers on. Subsequently a network operator's network isdetected and the Femtocell base station authenticates itself with thedetected network in step 210. As part of the authentication step theFemtocell base station obtains configuration parameters required for itsoperation within the network as well as a list of neighbouringFemtocells from the operator's Network Management System. The operatingparameters comprise parameters that enable the Femtocell base station toestablish a control channel for the exchange of control information withother Femtocell base stations connected to the operator's network. Instep 220 the Femtocell base station sends a query on the control channelinvestigating whether another entity, such as another Femtocell basestation, acts as a local resource manager. If in step 240 it isdetermined, for example based on the absence of an appropriate responseto the query, that the function of local resource manager is not beingperformed by another entity the process moves to step 250, in which theFemtocell base station assumes responsibility for local resourcemanagement and initialises a resource allocation table. Once theFemtocell base station has assumed responsibility for local resourcemanagement, the Femtocell base station continues to monitor the controlchannel (in step 260) for messages from other Femtocell base stationsand other channels for service requests from user equipment.

If another Femtocell base station powers up it will also send a querysimilar to the query sent in step 220. Such a query will be detected instep 260 and a response that the function of local resource manager isalready being performed may be sent in response. Notifications fromother Femtocell base stations are also detected in the monitoring step260. If no notification is received monitoring continues. Upon detectionof a notification in step 270 the Femtocell base station determines instep 280 whether or not the notification is a notification of the newallocation of resources, in which case the resource allocation table isupdated in step 290 and monitoring continues in steps 270 and 260. Ifthe notification is a notification of an interference the methodproceeds to steps 300 and 310, wherein a note is made of theinterference and the resource allocation table is consulted to identify,based on the knowledge of the resources that are being used by themanaged Femtocell base stations, which changes will most likelyeliminate or at least reduce the notified interference. The managedFemtocell base station or the managed Femtocell base stations that canmake the identified change in resource allocation is/are then notifiedvia the control channel to implement the identified resourcereallocation. Continuous monitoring for a response from the so contactedFemtocell base station(s) will yield a response, if the contacted basestation complies and notifies compliance. This permits an update of theresource allocation table in step 290 in the above described fashion.The process shown in FIG. 3 thus provides a means for local resourcemanagement in a network comprising a number of Femtocell base stations.

If in step 240 a message is received via the control channel indicatingthat the function of local resource manager is already being fulfilledby another Femtocell base station, then the process proceeds to steps320 and 330, where channels are being continuously monitored for servicerequests from user equipment. A local resource managing Femtocell basestation will notify the querying base station of its own list of localFemtocell base stations.

If a service request is received from user equipment one or moreresource blocks are allocated to the user equipment in step 340 toenable communication of the user equipment with the operator's networkvia the Femtocell base station. The allocation of the resource blocks isnotified to the local resource managing Femtocell base station in step350, so that the local resource managing Femtocell base station canupdate the resource usage table accordingly. In steps 360 and 370 acheck is performed to determine whether or not the local resourcemanaging Femtocell base station has acknowledged the notification of theresource block allocation. Once this notification has been received theFemtocell base station starts to monitor its channels in step 380 forthe receipt of expected periodic measurement reports from the userequipment. If no such measurement reports are received it is determinedin step 390 whether the service request of the user equipment has beencompleted. Should this not be the case, monitoring for service reportscontinues in step 380. Otherwise the local resource managing Femtocellbase station is notified of the completion of the service request instep 400, thereby enabling the local resource managing Femtocell basestation to update the resource usage table to indicate that the resourceblock that had been used for the user equipment service request are nolonger in use. Acknowledgement of the notification from the localresource managing Femtocell base station is again awaited in steps 410and 420 and, following receipt of this acknowledgement, the processreturns to step 320.

Should it be determined in step 380 that a periodic measurement reporthas been received from the user equipment, it is determined in step 430if this report indicates bad performance, for example because of thepresence of interference from another channel. Should the reportindicate satisfactory performance, the method returns to step 380 toawait the receipt of the next measurement report from the userequipment.

If the periodic measurement report from the user equipment, however,indicates that the performance is not satisfactory, then the localresource managing Femtocell base station is notified of the poor servicein step 450 and its response is awaited in step 460. In step 470commands received from the local resource managing Femtocell basestation in the response are implemented in the receiving Femtocell basestation and a notice of the completion of the implementation is againsent to the local resource managing Femtocell base station. A responseto the acknowledgement is then awaited (steps 480 and 490) and, oncereceived, the process returns to the monitoring for service requestsfrom user equipment in step 320.

The reader will appreciate that the parts of the process illustrated bymeans of steps 320 onwards relate to the operation of the Femtocell basestation relative to a single user equipment service request only.Femtocell base station may have the ability to parallel process aplurality of user equipment service requests and apply the steps of theFIG. 3 process following step 320 to a number of user equipment servicerequests. This part of FIG. 3 has nevertheless been limited to refer toa single user equipment service request only to improve the clarity ofillustration.

It will be appreciated from the above that the algorithm described withreference to FIG. 3 incorporates a number of features that may also beoperated independently from each other. In the FIG. 3 algorithm, theneighbouring list is, for example, provided by the network operator. Inan alternative arrangement, however, each Femtocell base station maycreate its own neighbouring list in an autonomous fashion, as describedin more detail below.

The FIG. 3 algorithm parameters for establishing the control channel aremoreover received from the network operator. The Femtocell base stationsmay alternatively establish a communicative link with neighbouringFemtocell base stations in an autonomous fashion (that is without inputfrom the network operator). A Femtocell base station that is arranged toalso operate in a WLAN infrastructure mode, for example, can communicateon the unlicensed spectrum and establish the control channel thereonwithout requiring input form the network operator.

Providing the control channel discussed above with reference to FIG. 3(as well as the control channel that will be discussed in more detailbelow with reference to FIGS. 6 and 8) enables communication betweenFemtocell base stations, so that attempts to overcome an interference,that may, for example, be experienced by user equipment operating withinan area covered by one or more of the Femtocell base stations, can takenot only the operating conditions of a single Femtocell base stationinto account (as is the case for known systems comprising a plurality ofFemtocell base stations) but the conditions governing the operation of aplurality or all of the Femtocell base station in communicative contactwith each other via the control channel.

It was realised that, if Femtocell base station that can interfere witheach other independently decide to reduce transmit power in an attemptto reduce interference the Femtocell base station itself may experiencedegraded performance. Independently acting Femtocell bases stations maythus be configured not to address interference problems that do notaffect their own performance.

It can be envisaged that two regions, each being managed by oneFemtocell base station acting as a local resource manager, overlap sothat one Femtocell base station can receive control commands from bothof the local resource managers (e.g. in step 460). As the two localresource managers may not communicate with each other, the receivedcommands may not be the same or may even be conflicting. The Femtocellbase stations may be arranged to sequentially execute such commands. Ifthe first commands successfully overcomes an interference situation,then the second command may not be executed and simply ignored.

It will be appreciated that a Femtocell base station that does notfulfil the function of a local resource manager does not need to beaware of the identities of the other Femtocell base stations that areunder the management of the local resource manager.

a Femtocell base station is located in an region that can communicatewith two Femtocell base stations that act as local resource managers

FIG. 4 shows a resource usage table as it may be maintained in the localresource managing Femtocell base station. As can be seen from FIG. 4 thetable has one column dedicated to each available resource block, withall available resource blocks being listed in the columns of the table.Each line of the table relates to one of the Femtocell base stationsmanaged by the local resource managing Femtocell base station. This ofcourse includes the local resource managing Femtocell base station aswell as any base stations that have later authenticated themselves withthe operator's network, discovered the resource managing Femtocell basestation and hence are communicatively coupled to the Femtocell basestation. As can be seen from the table in FIG. 4, a record of the use ofeach resource block by the Femtocell base stations is kept. While eachresource block may only be used by a single Femtocell base station itcan also be seen that some resource blocks are used by more than oneFemtocell base station. It can, for example, be seen that resource blockRB 0 is used by Femtocell base station 1 (Femto 1) as well as byFemtocell base station 3 (Femto 3). It is likely that resource blocksare simultaneously used by more than one Femtocell base station, inparticular during times of high communication traffic levels, given thatin the process shown in FIG. 3 the Femtocell base stations autonomouslyallocate resource blocks when initially responding to a user equipmentsservice request. Such simultaneous use of a resource block is not onlyacceptable, given that in many cases it is unlikely to create anyinterference or other performance degradation due to the difference incoverage area of different Femtocell base stations, but also desirableas it increases the bandwidth available from the managed Femtocell basestations. The interference management method described above withreference to steps 300 and 310 of FIG. 3 provides a way of improving theperformance experienced by a user equipment service request that may becaused by the simultaneous use of a resource block by two or moreFemtocell base stations.

When the local resource managing Femtocell base station receives anotification from a Femtocell base station of the allocation of aresource block in step 280 shown in FIG. 3 the local resource managingFemtocell base station updates the table shown in FIG. 4 by changing thetable entry relating to the notifying Femtocell base station and theresource block that has been notified as having been newly allocatedfrom “0” to “1”. Equally, should the local resource managing Femtocellbase station receive a notification that the use of a resource block hasceased, such as, for example, a notification sent in step 400 of FIG. 3,then the local resource managing Femtocell base station changes thecorresponding entry in the table from “1” to “0”.

It will be appreciated that the knowledge of the local use of thevarious resource blocks in the local resource managing Femtocell basestation enables the local resource managing Femtocell base station todetermine the likely source of an interference. The local resourcemanaging Femtocell base station may, for example, determine if aresource block that experiences interference is used by a Femtocell basestation other than the Femtocell base station providing service to theuser equipment experiencing the interference. If it is found that thisis the case, then one of the Femtocell base stations currently using theresource block may be instructed, for example in step 310 of FIG. 3, touse a different resource block.

Turning now to another embodiment, it has been discussed above that aFemtocell base station can generate its own neighbouring list. Anexample of such a neighbouring list is shown in FIG. 5A. As can be seefrom this figure, the neighbouring list comprises a number of IDs of theneighbouring Femtocell base stations from which the Femtocell basestation maintaining the list can receive messages. In the second columnof the list an indication of the strengths of the signals received fromthe individual neighbouring Femtocell base stations is provided. In theneighbouring list 300 the neighbouring Femtocell base stations arearranged in the order of descending signal strength, so that theneighbouring Femtocell base station with the strongest signal appearsfirst in the list and the neighbouring Femtocell base station with theweakest received signal appears last in the list. It will be appreciatedthat the stronger the signal received from the neighbouring Femtocellbase stations, the more likely it is that the neighbouring Femtocellbase station is the source of an interference. The neighbouring listshown in FIG. 5A thus provides a useful indication of likelyinterferers. It will moreover be appreciated that the order of the listis not essential. The neighbouring list may, for example, remainunordered or may list the neighbouring Femtocell base stations in anorder different from the order shown in FIG. 5A, for example in order ofascending signal strength.

FIG. 5B shows another, more detailed example of a neighbouring list. Thetwo leftmost columns of this list correspond to the two columns of theneighbouring list shown in FIG. 5A. In addition to the informationprovided in the list shown in FIG. 5A, the neighbouring list shown inFIG. 5B also comprises one column for each communication resource (inthis case resource block) available to the Femtocell base stationmaintaining the list for data transmission. The processor 150 shown inFIG. 2 notes the allocation of a resource block for data transmission,either if the processor 150 itself allocates such a resource block fordata transmission or if the Femtocell base station maintaining the listreceives a notification from a neighbouring Femtocell base stationindicating that the neighbouring Femtocell base station has allocated alisted resource block for data transmission. As can be seen from FIG.5B, the allocation of a resource block can be indicated by entering asimple “1” in the list, so that only one bit of memory space is requiredto track the allocation of each resource block for each of theneighbouring Femtocell base stations as well as for the Femtocell basestation that maintains the list.

It will be appreciated that the list shown in FIG. 4 could be maintainedalongside the list shown in FIG. 5A so that the combined informationcontent of these two lists corresponds to that of the list shown in FIG.5B. It will be appreciated that knowledge of the communication resourcesthat have been allocated to communication processes by neighbouringFemtocell base stations allows to avoid collision/the introduction ofinterference. Such knowledge thus provides an advantage over knownFemtocell base stations that allocate transmission resources withoutknowledge of the activities of neighbouring Femtocell base stations.Similarly, a known (isolated) Femtocell base station may decide toreduce its transmit power in light of a notified interference. If thisis done without coordinating with the interfering entity, the Femtocellbase station may continue to experience degraded performance if theinterfering entity does not adapt.

FIG. 6 shows a flowchart 600 for generating a neighbouring list, such asthe neighbouring list shown in FIG. 5A. After powering on in step 610,authenticating with the operator's network and receipt of configurationdata in step 620, the Femtocell base station advertises its presence toother Femtocell base stations that may be within transmission range viaa control channel established for this purpose (the operating parametersfor establishing this control channel may be received from theoperator's core network in step 620). The control channel is shared byother Femtocell base stations that have authenticated themselves in afashion similar to that of step 620 with the network operator. TheseFemtocell base stations listen for information traffic on the controlchannel and, if they receive the message the Femtocell base station hassent in step 630, send a response to the received message. NeighbouringFemtocell base stations also make a note of the signal strength of themessage sent in step 630, for example for entry in a list such as thelist shown in FIGS. 5A and 5B. Femtocell base stations may alternativelybe arranged to send regular or frequent beacons without expectation of aresponse from other Femtocell base stations. All beaconing Femtocellbase stations in a system can be included in a neighbouring list as longas the regular or frequent beacons are received and excluded from theneighbouring list once receipt of the beacons has stopped. The timeintervals at which any such beacons may be transmitted may bepredetermined in the Femtocell base station or may be changed later, forexample during use.

The Femtocell base station that has transmitted the message in step 630similarly listens for any responses from neighbouring Femtocell basestations and, if received, detects and stores an indication of thesignal strength of a received reply message in step 660. Replies fromneighbouring Femtocell base stations are sorted by signal strength instep 670, as discussed above.

The control channel is further utilised by the Femtocell base stationsto advertise the allocation of a resource block to data communication,for example with user equipment. Nodes receiving such allocationmessages can enter the received information in a table, such as thetable shown in FIGS. 4 and 5B, to keep track of those resource blocksthat are already being used. De-allocation of resource blocks canequally be advertised by the Femtocell base stations, so thatneighbouring Femtocell base station can update their respective resourceallocation lists to indicate a newly available resource block as beingfree.

After an arbitrary period of time the Femtocell base station may againadvertise its presence on the control channel in step 690, althoughdoing so may not be mandatory. Performing such a repeated advertisementis advantageous as it confirms that the Femtocell base station has notbeen deactivated. It will be appreciated that the algorithm illustratedby FIG. 6 enables a network of Femtocell base stations to keep up todate information regarding its neighbouring Femtocell base stations.This includes an ability of the Femtocell base station to readily adaptto the addition of further Femtocell base station or to the removal of aFemtocell base station.

It will moreover be appreciated that the above discussed distributedapproach to generating a neighbouring list is practicable for networkscomprising a large number of Femtocell base stations, as there is norequirement for interaction with the network operator in generating theneighbouring list. The bandwidth a network operator may make availablefor the configuration of Femtocell base stations is thus not used forgenerating the neighbour list and cannot therefore impose an upper limiton the number of Femtocell base stations in the network. Expressed moregenerally, the resource management burden on the network operator isreduced. As the neighbouring list is moreover generated by a wirelessinteraction between neighbouring Femtocell base stations the networkoperator's core network is moreover not overwhelmed by managementtraffic associated with the generation of the neighbouring lists.

Upon identifying interference the Femtocell base station may take stepsto mitigate or eliminate the interference and/or, avoid allocating thecommunications resource/resource block to communications starting withina predetermined time from the receipt of the notification.

The Femtocell base station may note the interference notification in aninterference list. An example of such an interference list is shown inFIG. 7. As can be seen from FIG. 7, the interference list can be asimple bit map that comprises one bit for each of N available resourceblocks. If the Femtocell base station maintaining the interference listreceives a notification of an interference, then the processor 150 canchange the state of the bit corresponding to the resource block from “0”to “1” to indicate that the resource block in question experiences aninterference.

Turning now to FIG. 8, FIG. 8 shows an algorithm 800 for operating adistributed resource allocation mechanism. In an initial step 810 theFemtocell base station operating its local version of the resourceallocation mechanism checks if a service request has been received fromuser equipment and, should this not be the case awaits receipt of such arequest in a loop created by waiting step 820. Following the receipt ofa service request from user equipment the Femtocell base station checksa resource allocation table (discussed above with reference to FIGS. 4and 5B) for free resource blocks that could be allocated to the servicerequest. Should any resource blocks be free, the resource block forwhich the user equipment experiences the best signal quality isallocated to the communication with the user equipment in step 850. Theresource allocation table is then updated to reflect the new allocationof the resource block and this new allocation is moreover advertised tothe neighbouring Femtocell base stations via the control channel in step860.

Should it be found in step 840 that no resource blocks are free, thenthe Femtocell base station considers, in step 870 and based on ameasurement report from the user equipment and on the above discussedresource allocation list, which resource block to allocate forcommunication with the user equipment. The processor 150 may, forexample, preferentially allocate those resource blocks used by aneighbouring Femtocell base station with low signal strength (as per theneighbouring list of FIG. 5A or 5B) to minimise the danger of causinginterference. Following the allocation of the resource block, theresource allocation table is again updated, in step 880, and theallocation is notified to other Femtocell base stations. It will beappreciated that the allocation of the resource blocks can also look tothe above discussed interference list and avoid allocating resourceblocks that are known to already suffer from interference.

Once a resource block has been allocated for the communication with theuser equipment, the Femtocell base station enables communication of theuser equipment with the operator's network and monitors for receipt ofperiodic measurement reports in step 890. If such measurement reportsare received at the Femtocell base station, and any such report is notdetermined in step 900 to not indicate unsatisfactory performance, thenthe Femtocell base station simply continues waiting for the next one ofthe periodic reports in step 910. Should a received report, however,indicate that performance is not satisfactory, then the algorithm moveson to step 920, in which the resource allocation table is investigatedto determine if there is a free alternative resource block that could beused for the communication session. Should this be the case the resourceblocks are reallocated, so that the free resource block is used infuture. The resource allocation table is updated to reflect thisreallocation in step 930 and the reallocation is also notified to theneighbouring Femtocell base stations in the above described manner. TheFemtocell base station may introduce a delay between steps 920 and 930.This delay may have a random length, so that two Femtocell base stationsof the same type are unlikely to act simultaneously. Following the delaythe receipt of a further periodic measurement report may be awaited todetermine whether or not performance has been improved by another(faster action or less delayed) Femtocell base station. Should it befound that performance has been improved to a satisfactory level, thenstep 930 may not be needed and the algorithm can instead return to step890.

If it is determined in step 920 that no spare resource blocks areavailable, then a resource block that is already being used by aneighbouring Femtocell base station is used instead of the resourceblock that is currently in use. For this purpose it is determined whichof the neighbouring Femtocell base stations is the least potentialinterferer in step 940. This can be done by considering the signalstrength information in the neighbouring list of FIG. 5A. The leastpotential interferer is the neighbouring Femtocell base station forwhich the lowest signal strength has been measured. In the table shownin FIG. 5A this is the Femtocell base station that is last in the list.

Once the least potentially interfering Femtocell base station has beenidentified the Femtocell base station operating the algorithm 800 ofFIG. 8 negotiates the transmit power the Femtocell base stationimplementing the algorithm 800 of FIG. 8 uses for the resource block inquestion and the transmit power used by the least potentiallyinterfering Femtocell base station uses for the resource block inquestion. If the least potentially interfering Femtocell base stationhas not changed since the receipt of the service request from the userequipment and no resource blocks were initially available for allocationto the service request, then the resource block used is the same as theresource block used by the least potentially interfering Femtocell basestation. In this case the selected resource can be used further and theFemtocell base station operating the algorithm 800 of FIG. 8 negotiates,in step 950, the transmit power with the least potentially interferingFemtocell base station that both base stations use for communicationusing the resource block in question. If the least potentiallyinterfering Femtocell base station has changed, then the resource blockused by the Femtocell base station operating the algorithm 800 and theresource block that is least likely to cause interference differ fromeach other. In this case the resource block used for communicating withthe Femtocell base station is changed to the resource block used by theleast interfering Femtocell base station and the transmit power used byboth Femtocell base station for transmission using the newly selectedresource block is negotiated and adopted in step 960.

If it is determined in step 890 that no periodic measurement reports arereceived from the user equipment, then it is checked in step 970 whetheror not the user equipment's service request has been completed. Shouldthis not be the case, then the algorithm simply returns to step 890 toawait the next periodic measurement report. If the service request hasbeen terminated, then the resource allocation table is updated in step960 to reflect that the resource block used for the service request hasbeen freed (e.g. by setting the corresponding bit in FIG. 5B to “0”).The Femtocell base station moreover broadcasts the fact that thisresource block is no longer in use to the neighbouring Femtocell basestations via the control channel.

It will be appreciated from the above that the Femtocell base stationscan act as a standalone device that does not need to share backupservices with other Femtocell base station to create the neighbouringlist, an interference list or a resource allocation list. A systemcomprising a number of the above described Femtocell base stations canthus be a fully distributed system, in particular a system that does notrequire the use of a centralized server to coordinate or storeinformation on the geography of the Femtocell base stations.

Turning now to the manner in which neighbouring Femtocell base stationscommunicate with each other, as discussed above, the Femtocell basestation establish a control channel through which the relevantinformation/messages can be exchanged. The information/messages can beexchanged periodically or upon start-up. If the exchange is periodical,then each Femtocell base station periodically announces its presence, sothat the neighbouring Femtocell base stations within range can updatetheir neighbouring lists appropriately. It can be envisaged that, if anetwork of Femtocell base stations is operated in this manner, eachFemtocell base station may automatically delete another Femtocell basestation from its neighbouring list if no message indicating thecontinuing presence of the other Femtocell base station is received fora predetermined period of time. This period of time may be longer than asingle period required for receipt of such a message and may be longerthan two such periods to allow for loss of one of the scheduledmessages. Alternatively the Femtocell base station can advertise theirpresence only upon power up. In this case each Femtocell base stationretains information of the presence of neighbouring Femtocell basestations in its memory.

The Femtocell base station may further announce the communicationresource they use to the neighbouring Femtocell base stations. This canagain be done by periodical transmission of a list of the resourceblocks used (in which case the resource blocks for which no periodicnotification is received after some time can be marked as free).Alternatively the use of a resource block can be announced to theneighbouring Femtocell base station once the use has commenced. In thiscase the Femtocell base station may send a separate announcementinforming neighbouring Femtocell base stations once the resource blockis no longer in use. Each node that receives a message can rank theneighbouring node from which the message was received based on theattributes of the received message.

Turning now to the establishing of a control channel by the Femtocellbase station in situations where the network operator does not providethe operating parameters for such a control channel, one problem inimplementing the control channel is contention, as the deployedFemtocell base stations are uncoordinated, as least prior to theestablishing of the control channel. One way of limiting incidences ofcollision is to use a carrier-sense multiple access scheme (CSMA).Implementing a CSMA scheme in practice requires only a relatively simpleprotocol. In all but the most pathological scenarios and deployments astraightforward solution is likely to deliver a workable system providedthat the occasional missing piece of knowledge is expected and cateredfor.

A distributed broadcast mechanism may alternatively be implemented. TheIEEE 802.11 WLAN system, for example, allows each device in the basicservice set to take turns (on a probabilistic basis) to send a broadcastbeacon.

In the WiMedia/IEEE 802.15.3a (WiMedia-Alliance, “Standard ECMA-368 HighRate Ultra Wideband PHY and MAC Standard,” ed. Geneva: EcmaInternational (Ecma), 2005) a more distributed approach is adopted (alsoto support the distributed resource reservation system) in which thebeacon phase of the repeating super-frame includes a series of slots toallow each member device to broadcast its own “mini beacon” advertisingits resource reservation. A newly joining device takes the nextavailable beacon slot. Mechanisms are defined within the standard todeal with beacon clashes (e.g. as a result of two newly arrivingdevices, or a device hidden from another, choosing the same slot). Suchan approach has also been documented in the EPRMA protocol (J. del PradoPavon, et al., “The MBOA-WiMedia specification for ultra widebanddistributed networks,” IEEE Communications Magazine, vol. 44, pp.128-134, June 2006). This offers another possible solution.

One way of determining the potential of a neighbouring Femtocell basestation to interfere is measuring the strength of a signal received fromthe Femtocell base station, as discussed above. The neighbouringFemtocell base stations can be ranked in ascending/descending order ofreceived power to identify likely interferers. To allow such ranking theFemtocell base stations may use a standard/predetermined power level fortransmission on the control channel. In general, based on thesemeasurements and other available information such as feedback from userequipment, the base stations will allocate frequencies in the mannerwhich will best satisfy a predetermined criterion. An example of such acriterion is minimizing interference to neighbouring cells, or a balanceof maximizing throughput and minimizing interference. The lattercriterion can be expressed as:

${\arg\;{\max\limits_{i}{\alpha\;\gamma_{i}}}} + {\left( {1 - \alpha} \right)\frac{\Gamma}{\sum\limits_{k = 1}^{N}{a_{k}\delta_{k,i}}}}$

where α is the regularization parameter that may be used for eitheremphasising signal quality or reducing interference, γ_(i) is the signalstrength of the ith resource block which is fed back by the userequipment, Γ is a scaling constant, chosen to prevent the second termfor unduly influencing the sum. If for example, weak signals arereceived from all neighbouring Femtocell base stations, then the secondterm may become large, causing the selection of a resource block withpoor quality. The use of the scaling constant Γ helps to avoid thisdanger. a_(k) is the signal strength from the kth neighbouring node (outof N neighbours) or a normalised signal strength from the kthneighbouring node, and δ_(k,i)ε{0, 1} is the assignment indicator ofresource block i at the kth neighbouring node.

It will be appreciated that the above description of specificembodiments has been made by way of example only and that thisdescription is not intended to be a limiting one. It will be appreciatedthat some modification to the arrangements described with regard to thefigures are possible. It is, for example, envisaged that local resourcemanaging Femtocell base stations or any of the Femtocell base stationsoperating in the above described distributed arrangement may also keep arecord of previous interference problems, of the steps taken in anattempt to rectify such problems and of whether or not taking thesesteps has improved performance. A record of this type can provide anindication of likely interference pattern between Femtocell basestations. Such a record may help in reliably determining whichinterference pattern is being experienced in a new interferencenotification and may thus be useful in expediently finding a manner inwhich such a new interference can be reduced or removed.

In the above described embodiment the local resource managing Femtocellbase station sends instructions/commands for the re-allocation ofresource block. In an alternative arrangement the local resourcemanaging Femtocell base station may instead or additionally send apolicy by which the receiving Femtocell base has to structure resourceallocation.

While certain embodiments have been described, the embodiments have beenpresented by way of example only, an area not intended to limit thescope of the inventions. Indeed, the novel methods, apparatus andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the inventions. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the inventions.

The invention claimed is:
 1. A Femtocell base station configured tocommunicate with one or more Femtocell base stations in a communicationnetwork using a control channel for exchange of control information, thecontrol channel established via an air interface, and the Femtocell basestation configured to act as a central resource manager to co-ordinate aresponse to an interference event experienced within an area of coverageof another Femtocell base station in the communication network by beingconfigured: to receive interference notifications from the otherFemtocell base station via the control channel, to determine, using arecord of resource blocks that have been allocated by other Femtocellbase stations, an action for reducing or eliminating an interferencenotified in the interference notification, and to send an interferenceremedial command to at least one of the other Femtocell base station andone or more further Femtocell base stations in the communicationsnetwork via the control channel, wherein the interference remedialcommand is a command for execution by at least one of the otherFemtocell base station and the one or more further Femtocell basestations that, when executed by the other Femtocell base station and/orby the one or more further Femtocell base stations, puts the action intoeffect, wherein the action includes changing an allocation of a resourceblock by the other Femtocell base station and/or by the one or morefurther Femtocell base stations or altering a transmit power used by theother Femtocell base station and/or by the one or more further Femtocellbase stations.
 2. A system comprising: a plurality of Femtocell basestations, all in communicative contact with each other via acommunication network; a first Femtocell base station configured to actas a central resource manager and to communicate with other Femtocellbase stations in the plurality of Femtocell base stations using acontrol channel for exchange of control information, the control channelestablished via an air interface, the first Femtocell base stationfurther configured to receive an interference notification from anotherFemtocell base station via the control channel, and to co-ordinate aresponse to an interference event experienced within an area of coverageof the another Femtocell base station in the communication network; anda second Femtocell base station; wherein the first Femtocell basestation is further configured to determine, using a record of resourceblocks that have been allocated by other Femtocell base stations in thecommunication network, an action for reducing or eliminating aninterference notified in the interference notification and to send amessage, comprising a command to the second Femtocell base station viathe control channel to put the action into effect, the action includingchanging an allocation of a resource block by the second Femtocell basestation or altering a transmit power used by the second Femtocell basestation.
 3. A system according to claim 2, the first Femtocell basestation further configured to receive messages identifying aninterference in data transmission.
 4. A method of managing interferencein a system comprising a plurality of Femtocell base stations all incommunicative contact with each other via a communication network, themethod comprising: receiving, by a first Femtocell base stationconfigured to act as a central resource manager and configured tocommunicate with other Femtocell base stations in the plurality ofFemtocell base stations using a control channel for exchange of controlinformation, the control channel established via an air interface,interference notifications from the other Femtocell base stations viathe control channel; co-ordinating a response to an interference eventexperienced within an area of coverage of another Femtocell base stationin the communication network; determining, in the first Femtocell basestation using a record of resource blocks that have been allocated byother Femtocell base stations, an action for reducing or eliminating theinterference event; and sending a message from the first Femtocell basestation to another Femtocell base station in the communication network,the message comprising a command for execution by the other Femtocellbase station, the command when executed by the other Femtocell basestation putting the action into effect, wherein the action includeschanging an allocation of a resource block by the other Femtocell basestation or altering a transmit power used by the other Femtocell basestation.
 5. A method according to claim 4, further comprisingdetermining a source of interference using a record of resource blocksthat have been allocated by the plurality of Femtocell base stations. 6.A method according to claim 4, further comprising: receiving at theother Femtocell base station the message comprising a command that, whenexecuted in the Femtocell base station, puts into effect the actioncausing a change in at least one of an allocation of resource blockswithin the Femtocell base stations and a transmit power level used forcommunicating with user equipment; and executing the command in theother Femtocell base station.